Bài 4 : 1,x^6-y^6=(x^3+y^3)(x^3-y^3)=(x+y)(x^2-xy+y^2)(x-y)(x^2+xy+y^2)
3, x^3-3x^2+3x-1-y^3
=(x-1)^3-y^3=(x-y-1)[(x-1)^2+y(x-1)+y^2]
=(x-y-1)(x^2-2x+1+xy-y+y^2)
=(x-y-1)(x^2+y^2+xy-2x-y+1)
4,(a+b)^3-(a-b)^3
=(a+b-a+b)(a^2+b^2+2ab+a^2-b^2+a^2+b^2-2ab)
=2b(3a^2+b^2)